直流偏磁增大换相失败风险的机理分析及仿真

Mechanism analysis of DC-bias increasing the risk of commutation failure

对直流偏磁、电压畸变导致过零点漂移以及与换相失败的关系进行了分析,指出直流偏磁场景下换流变压器的励磁电流将发生畸变,使得变压器励磁电抗工作在非线性区域,不仅可能引起交流母线电压的畸变以及换相线电压过零点漂移,甚至可能增大换相失败的风险.基于所建立的中国南方电网交直流混联输电系统PSCAD/EMTDC仿真模型,对特高压直流输电双极平衡和大地-单极运行工况下同一故障场景的换相失败风险进行了仿真分析和对比,结果验证了理论分析的正确性.

The relationship among direct current（DC）bias,zero-crossing shifting resulting from voltage distortion and commutation failure was analyzed in this paper.It was pointed out that magnetizing current of converter transformer distorted when DC biasing,resulting in the transformer magnetizing reactance working in the nonlinear region,which not only would cause the distortion of AC bus voltage,but also increase the risk of commutation failure.Based on PSCAD/EMTDC simulation software,China Southern Power Grid AC-DC Parallel Transmission System was established.By means of this model,simulations and comparison of ultra-high voltage DC transmission commutation failure risk of both bipolar balance and earth-unipolar operating conditions in the same fault scene were taken.The correctness of the theoretical analysis was proved by the simulation results.